The present invention relates to a method of fabricating integrated circuits, or more in particular to a method of fabricating integrated circuits in which the yield rate of the integrated circuits is improved by replacing a defective block with a spare block.
As a method of improving the yield rate of the integrated circuits, the redundancy method using fuse means for a semiconductor storage unit is well known. In this redundancy method, a normal memory cell and a spare memory cell are built on the same chip. In the case where a defect occurs in the normal memory cell, the function is saved by replacing the normal memory cell with the spare memory cell. The replacement of the normal memory cell with the spare memory cell is effected by blowing out the fuse and thus switching a decoder circuit activated thereby.
A redundancy method using the above-mentioned fuse means is disclosed, for example, in JP-A-1-98198.
On the other hand, JP-A-57-35342 discloses a method of fabricating large-scale integrated circuits in which the electric characteristics of a plurality of functional blocks are inspected by connecting functional blocks and interactive wires by connective wires. After that, only the connective wires of the functional blocks having unsatisfactory characteristics are eliminated, thereby constructing the desired system function by functional blocks with satisfactory characteristics.
In the microprocessor, the gate arrays, ASICLSI, etc., it is feared that the yield rate decreases considerably with the increased integration using the microprocessing technique. However, the problem is that the redundancy method using the above-mentioned fuse means is inapplicable to the integrated circuits other than the semiconductor storage devices. This fact is described below.
Integrated circuits other than the semiconductor storage devices have no circuit for selecting repeated blocks such as a decoder circuit which selects a memory cell of the semiconductor storage device in the presence of the repeat of same blocks. As a result, even when the repeated blocks have a spare block, a circuit for selecting repeated blocks is necessary to eliminate defective blocks and replace them with normally-operating blocks. The result is an increased circuit scale. Also, individual switching circuits are difficult to include due to the great variety of blocks.
The speed of IC is greatly reduced by increasing propagation delay due to switching blocks.
The method of fabricating large-scale integrated circuits disclosed in JP-A-57-35342, on the other hand, poses the defect that the constructed system function is restricted in spite of the fact that functional blocks having defective characteristics are separated to build the desired system.
Accordingly, it is an object of the present invention to provide a method of fabricating integrated circuits in which defective blocks are replaced by satisfactory blocks without any block-selecting circuit, and the yield rate of the integrated circuits is improved while at the same time improving the freedom of the functions of a built-up system.
In order to achieve the above-mentioned objects, a representative embodiment of the invention represents a method of fabricating integrated circuits, comprising a first stage for testing a plurality of circuit blocks by connecting a plurality of circuit blocks of a first conductor wire (hereinafter referred to as the temporary wire) and discriminating normal circuit blocks from the defective blocks, a second stage for removing the first wire (temporary wire), and for forming a second wire (hereinafter referred to as the main wire) (see FIG. 1) connecting the normal blocks to each other.
A preferred embodiment of the invention further shows the detail of a method of fabricating integrated circuits,
wherein semiconductor devices (N+, P) making up a plurality of circuit blocks before the first stage are formed in a semiconductor substrate (66), after which an insulating surface protection film (65) having a via on the semiconductor device is formed on the semiconductor device;
wherein prior to the first stage, an electrode (63) is connected to the semiconductor device (n+, P) through the via on the insulating surface protection film (65);
wherein an insulating film (64) having a via and made of a material different from the insulating surface protection film (65) is formed on the electrode and the insulating surface protection film (65) prior to the first step;
wherein the first conductor wire is connected to said electrode (63) through said via of the insulating film in the first stage; and
wherein the insulating film (64) is removed before the second conductive wire is formed in the second stage (See FIG. 6).
A preferred embodiment of the invention shows a further detail of the method of fabricating integrated circuits, in which the material of the first wire is different from that of the electrode (63) of the semiconductor device (n+, P) (See FIG. 6).
The first wire (temporary wires 61, 62) removed in the process is preferably made of a wire without remainder (such as a conductive material mainly composed of aluminum, tungsten or copper, or high-purity aluminum not containing silicon). Also, the insulating film (64) for the temporary wires (61, 62) is preferably composed of a material (an insulating material having the impurities content of less than 100 ppm and a heat resistance of 200.degree. C., such as polyimide) which does not damage the underlying insulating surface protection film (65) or the electrode (63) of the underlying semiconductor device in removing the insulating film (64) and the temporary wires (61, 62) (See FIG. 6).
According to the above-described process for fabricating integrated circuits, the conductor wire (temporary wire) connected for the block test can be removed. Therefore, in the case where a defective block is found, it can be removed for reconnection only with a satisfactory block.
As a result, the need of the circuit for selecting a block is eliminated and a defective block can be replaced with a conforming block, thereby providing completely satisfactory integrated circuits.
Also, since the wiring freedom of the second conductor wire (main wire) formed after removing the first conductor wire (temporary wire) is so large that the freedom of the functions of the system constructed is improved (See FIG. 1).
In a method of fabricating integrated circuits according to a preferred embodiment of the invention, the insulating surface protection film 65 and the insulating film 64 have different materials. In removing the insulating film 64 before forming the second conductor wire, therefore, the underlying insulating surface protection film 65 is rarely damaged (See FIG. 6).
In a method of fabricating integrated circuits according to a more preferred embodiment of the invention, the material 61, 62 of the first conductor wire is different from that of the electrode 63 of the semiconductor device. In removing the material 61, 62 of the first conductor wire as a temporary wire before forming the second conductor wire making up a main wire, therefore, the electrode 63 of the semiconductor device in the underlying block is seldom damaged (See FIG. 6).